Excavations on unpromising mounds in the Iraqi desert revealed Sumer’s earliest city. Surviving relics and a rebuilt temple have given experts more clues about the ancient metropolis of Eridu.

It appears that the culprit at Tall el-Hammam was a small asteroid similar to the one that knocked down 80 million trees in Tunguska, Russia in 1908. It would have been a much smaller version of the ...